In the past, no significant progress has been made to use the heat generated by internal combustion engines to heat a liquid medium. For instance, in carpet cleaning systems, where heated cleaning solution is required, the use of an internal combustion engine is highly desirable because it gives off significant heat energy which can be transferred to heat the cleaning solution. Furthermore, an internal combustion engine is fully portable and is not dependent upon an alternate power source so that it is suited to a mobile carpet cleaning system.
One of the few exceptions to the prior art discussed above is U.S. Pat. No. 4,109,340 issued Aug. 29th., 1979 to Leonard Eugene Bates, disclosing an arrangement in which the cleaning fluid itself, is used as the engine coolant and as such, picks up heat from the lubricating oils in the engine. The Bates Patent further goes on to disclose that some type of use may be made of the exhaust heat to further heat the coolant if necessary.
Although the Bates system is an advance over the prior art, it still suffers from some serious drawbacks. Firstly, the cleaning agents added to the cleaning solution are generally considered to be extremely caustic and as such, detrimental to the engine. Secondly, because the cleaning solution actually replaces the coolant in the Bates system, it runs throughout the engine and picks up contaminants in the cooling system. As anyone who has flushed an engine rad will appreciate these cooling systems, particularly through corrosion, become extremely dirty. From this standpoint, the Bates' system is no different from any other conventional rad cooled system, thereby presenting obvious contamination of the cleaning solution problems.
With regards to the use of the exhaust for heating the cleaning fluid, Bates makes no more than a mention that the exhaust gases developed by the engine can be used when desired for some additional heating of the coolant cleaner. Nothing further is disclosed with respect to what mechanisms are used to control the heat exchange from the exhaust gases to the cleaning fluid. Furthermore, because the exhaust is the area in which the greatest heat is generated from the engine, it would be desirable to have a system which relies primarily on the exhaust for efficiently heating the cleaning fluid of the carpet cleaning system.
The present invention provides such an arrangement without suffering from any of the drawbacks disclosed above and at the same time, making the best use of the heat given off by an internal combustion engine. The present invention's system relies upon heat exchange from the engine exhaust to heat a fluid medium which is conducted through an exhaust heat exchanger and maintained at all times in its own fluid conduit out of contact with the contaminant exhaust gases.
The exhaust gases of the internal combustion engine provide enough heat to raise the temperature of the fluid medium to unacceptably high limits if left uncontrolled. Furthermore, for some job applications such as carpet cleaning, it is desirable to maintain the medium in the liquid state.
The system is therefore, further provided with temperature sensing means when the temperature of the fluid medium from the heat exchanger has reached a predetermined desired level as well as controls responsive to the temperature sensing means for ensuring that the temperature of the fluid medium does not exceed that desired level.
Examples of these controls could include a bypass at the heat exchanger which is operated by the temperature sensing means to bypass the heated exhaust away from the heat exchanger and/or automatic shutdown controls to shut the entire system down in the event of system malfunction.
Unlike the Bates system, the present invention does not require heating of the fluid medium directly at the engine block, although this may be used as a preheat prior to reaching the exhaust heat exchanger if desired. However, even when the preheat is used in the present invention it is completely different from the Bates system, in that the fluid medium is not used as the engine coolant but rather, is again carried in its own cleaning fluid conduit through a heat exchanger, into which the heated engine coolant is directed. The fluid medium of the present invention is therefore, maintained free of impurities which would otherwise be picked up from the engine block and as such, has maximum efficiency as a cleaning agent.